melted away, leaving the finished product. While this resulting product is more
accurate than a simple SLA part, the surfaces still need to be polished after printing to create a fully transparent part.

Researchers at Formlabs, a 3D printer
company in Somerville, Mass., developed
a unique way to polish their 3D-printed
lenses. They molded a small rod on one
end that fits into the chuck of a power
drill, which simplifies the polishing procedures. The powered process makes it
easier to polish, creates more uniform
parts and allows less material to be
removed.

PolyJet prints with a photopolymer
that’s instantly cured with UV light.
This process uses two jetting heads to
print the desired part and its support
structure. The part is built layer-by-layer
and requires a post-processing step to
become smoother and more optically
transparent.

3D-printed light pipes

Researchers have built several other
types of optical components in 3D-print-
ing processes that don’t require the
strict optical transparency specifications
demanded in lens-type devices. One of
these designs is embedded optical fibers
within a rigid object. These optical fibers
exploit the component’s total internal
reflection to guide light within the object.
This work was performed by researchers in the Computational Design Lab at
the Human-Computer Interface (HCI)
Institute of Carnegie Mellon Univ., Pittsburgh, in collaboration with researchers at
Disney Research Pittsburgh. These printed
optics enable sensing, display and illumination elements to be directly embedded
in the casing or mechanical structure of
a 3D-printed interactive device. These
3D-printed “light pipes” enabled the construction of unique display surfaces, novel
illumination techniques, custom optical
sensors and embedded optoelectronic components.

These devices were 3D printed on anObjet Eden (Stratasys) 260V 3D printerwith Objet VeroClear transparent mate-rial for the construction of the opticalelements. VeroClear has similar opticalproperties to PMMA (polymethyl meth-acrylate), which is widely used for other

3D-printed optical components. It has a
refractive index of 1.47. The 3D printer
has a print resolution of 600 dpi, which is
several times finer than other commonly
available 3D printers. This allowed the
optical components to be smooth, without
any internal gaps.

While these “light pipes” can be 3D
printed in any configuration and complexity, prefabricated optical components
can also be dropped into the 3D-printing
process.

Silicone optics

3D-printing processes can also be
used to support the rapid prototyping
of optical components manufactured
from materials not yet usable in current 3D-printing equipment. One such
material is liquid silicone rubber (LSR).

Protolabs, Maple Plain, Minn., recently announced the molding availability
of optical-grade LSR. There are many
advantages for optical-grade LSR molded parts, not the least of which is its
transparency, which is 94% compared
to the 95% light transmission index of
the best glass across both the visible
and UV spectrum.

Its light weight and high flexibility, however, are what provides users
with even larger advantages over glass
optical components. Often, devices
fabricated from optical-grade LSR
don’t need gasketing to protect them
from the environment—their inherent
flexibility provides a built-in gasketing
capability, thereby reducing cost and
manufacturing complexity. “These
materials also have high thermal operating characteristics, up to 200 C, giving them a great advantage over most
other polymers,” says Jeffrey Schipper,
Protolabs product manager for LSR.
This high-temperature capability
is especially important for use with
high-output LEDs, which can generate
a reasonable amount of heat, although
not as much as equivalent incandescent
filaments.

Optical-grade LSR’s strong UV sta-bility, non-yellowing and inherent flex-ibility make it ideal for use in outdoorapplications, much more than otherbrittle polymers. LSR-molded parts alsocure without the inherent sinks, shrink-age and molded-in stresses associatedwith other molded polymer parts. Partscan also be molded in polished mold,without the need for secondary polishingoperations.

But LSR is a two-component thermosetting polymer, making it not currently
amenable to direct 3D-printing techniques.
LSR fabrication can still take advantage of
3D printing by first making a 3D model
of the desired optical part with conventional 3D-printing techniques—even
using opaque materials. A mold can then
be cast around this 3D-printed part and
then hand-filled using a caulking gun. The
resulting parts can be used for testing form
and fit, with limited numbers even used
with LSR materials.

The stiffness of optical LSR allows it to be used in vehicle lenses where lights are exposed to various vibrations and shocks.

Optical LSR’s high operating temperature, UV stability and
flexibility allow it to be used for outdoor applications.